Apparatus for reducing the wave making resistance for boats



MICHINORI KURIHARA 3,125,977

APPARATUS FOR REDUCING THE WAVE MAKING RESISTANCE; FOR BOATS I March 24, 1964 Filed Nov. 23, 1960 4 Sheets-Sheet 1 I myENTpR.

March 1964 MlCHlNORI KURIHARA 3,125,977

APPARATUS FOX-REDUCING THE WAVE MAKING RESISTANCE FOR BOATS Filed Nov. 23, 19 0 4 Sheets-Sheet 2 INVEN TOR.

APPARATUS FOR REDUCING THE WAVE MAKING RESISTANCE FOR BOATS Filed Nov. 25. 1960 M r h 1964 MICHINORI KURIHARA 4 Sheets-Sheet 5 INVENTOR- March 24, 1964 MlCHlNORl KURIHARA 3,125,977

APPARATUS FOR REDUCING THE WAVE MAKING RESISTANCE FOR BOATS Filed NOV. 23, 1960 4 Sheets-Sheet 4 FRO D N0.

WITHOUT JE E g" 41R ONLY \JETTD I500 r ATER ONLY Jarret) D p WATER /MED =3 M? A \JETl'E-D L000" 87 I,

. t m x Q. 500'- a INVENTOR.

Unitcd States Patent The present invention relates to a method of and apparatus for reducing the wave making resistance for boats, and in particular such means which enable a safe and high speed for the running of the boat with the least power by means of reducing the wave making resistance caused by the running of the boat.

It is one object of the present invention to provide an apparatus for reducing the wave making resistance for boats which includes a slit for fluid ejection at the bottom or the side of the hull and a fluid is ejected from the slit in order to even the pressure distribution of the Water stream to the exterior surface of the hull, whereby a mixture of air and water, especially sea water is used as the fluid, by making use of the high density of water.

It is another object of the present invention to provide an apparatus as set forth above, wherein the slit is provided near the bow of the boat.

It is a further object of the present invention to provide an apparatus as set forth above wherein the fluid is fed from an air compressor to the slit for air ejection, the air compressor being disposed at the bottom of the hull.

It is yet another object of the present invention to provide an apparatus as set forth above which includes an ejection chamber disposed at the bottom of the hull and an ejection slit facing the stern of the boat is provided, in order to disperse the fluid drawn from the air compressor by the guide wall into the water stream.

It is also another object of the present invention to provide an apparatus as set forth above wherein the slit is disposed within a range of 15% to 35% of the length of the boat measured from the bow of the boat.

It is a still further object of the present invention to provide an apparatus as set forth above which includes an intake at the side or bottom of the hull for feeding sea water to a pump and which includes an ejection chamber containing a guide wall for guiding the ejected water to the slit.

It is yet another object of the present invention to provide a method of reducing the Wave making resistance for boats which comprises the steps of ejecting water and air against the waves hitting the boat.

It is also an object of the present invention to provide a method as set forth above wherein two fluids are fed by a U-shaped guide vane.

With these and other objects in View, which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevation of a boat indicating schematically the pressure distribution without reduction of the wave making resistance;

FIG. 2 is a side elevation of the boat showing schematically the pressure distribution, however, with a reduction of the wave making resistance;

FIG. 3 is a side elevation of the boat indicating the apparatus for reducing the wave making resistance;

FIG. 4 is a front elevation of the hull of the boat, partly in section, indicating the apparatus for reducing the wave making resistance, the right section being'a view from the bow and the left section being a view from the midway section;

FIG. 5 is a side elevation of the hull disclosed in FIG. 4;

FIG. 6 is a fragmentary side view of the boat indicating the part of a slit for ejection;

FIG. 7 is a View seen from the stern of the boat showing the part indicated in FIG. 6;

FIG. 8 is a top plan view of the part shown in FIG. 6;

FIG. 9 is a side view of the part of a slit for ejection in case a mixed fluid of air and sea water is used;

FIG. 10 is an elevation of the part shown in FIG. 9 seen from the stern of the boat;

FIG. 11 is a top plan view of the part referred to in FIG. 10;

FIG. 12 is a schematic fragmentary view indicating the part of the manifold;

FIG. 13 is a side view of the part shown in FIG. 12;

FIG. 14 is the resistance curve diagram resulting from the application of the method of the present invention; and

FIG. 15 shows a diagram indicating the relations between the speed of the boat and the full engine power.

There are encountered, generally speaking, two water resistances to a running boat:

The frictional resistance of water to the hull of the boat and the wave making resistance caused by the uneven distribution of water pressure are encountered.

Referring now to the drawings, to explain the wave making resistance during the movement of the boat, water is plowed by the bottom C near the bow, as shown in FIG. 1 and splashes in front of the vessel, then makes billows alongside the vessel. This happens in the following manner: The speed of a stream of water suddenly decreases around the bottom C of the vessel and the water pressure thereabout rises according to Bernoullis theory, whereupon the high pressured water is rapidly put out to make streams in front of and alongside the vessel and thus causes a bow wave. As the angle of elevation of the bottom of the vessel increases on account of the rise in water pressure around the how, the wave making action becomes more and more active.

The present invention aims at the reduction of the wave making resistance, when a hull is moving and properly solves the problem of frictional resistance, enabling the boat to move safely at a high speed utilizing its energy effectively.

To explain the illustrated structures, in which the present invention has been adopted, FIGS. 4 and 5 illustrate a hull A which is provided with a propeller 4 having for instance three blades. The blades are arranged at equal distances and secured to the propeller shaft 5, which is supported by a supporting frame 3 at the stem 2.

In order to perform the method of the present invention, an ejection chamber 11 is provided at the bottom of the bow with an ejection part 8, as illustrated in FIGS. 6 to 8. Thus the structure is designed in such manner that the guide pipes 7 for the air supply are set on both sides of the keel line 1 from the centrifugal air compressor 1% to be driven by a gas-turbine 15 (FIG. 5). Thus, a slit 10 for ejection is formed along the bottom of the boat. The guide pipes 7 for the air supply are, respectively, connected with the mentioned centrifugal air compressor 16 and compressed air is effectively ejected along the bottom surface of the boat.

The place for the opening of the slit, illustrated in FIGS. 5 to 8, as mentioned above, is, for example, at a distance of l m. (in. standing for meter) from the point where the bow wave height is at its maximum and the said point is at a distance, for example, of about 5 m. from the bow.

In. order to perform in accordance with the method of the present invention, the use of a special gas or liquid is considered, but air or water, especially sea water is preferably used, because a considerable amount of fluid is required. Moreover, a mixture of fluids are used, be-

sides independent use of air or water and particularly in case of use of a mixture, the nearer the distance between the speeds of the jet and of the movement of the boat, the higher is the efiiciency of the jet effect. Lower speed of the water stream is enough to produce a certain power for higher density of water. Consequently, it is better to use sea water than to use air only. On the other hand, the use of air is preferable to the use of water trom a view point of reducing the friction resistance. Thus, an excellent effect is obtained by using a mixed fluid. For the use of such mixed fluid, sea water is taken in the guide channel for the sea water or a guide slit is set on the outside at a part of the hull and after the water is properly subjected to pressure, it is guided to the opening of the outlet. Such guide channel, etc., as mentioned above, performs also the function of the wave making resistance reduction mechanism.

Referring now again to the drawings, and in particular to FIGS. 9 to 13, in case of the use of a mixed fluid consisting of sea water and air, sea water as a main fluid is guided to the ejection chamber and is ejected through a slit (for ejection by means of a guide vane or the like. When the sea water stream passes the guide vane, air is jetted into the sea water stream from the opening of the other slit tor ejection provided in the sea water stream. In order to explain the showing in the drawing, the intake 17 of sea water opens on both sides of the bottom of the hull A. The guide pipe -18 with the intake 17 of sea water is connected with the pump 2% to be driven by the prime mover mechanism. The opening 2 2 of the outlet pipe 21 from the pump 2%, in the same manner as shown in FIGS. 4 to 8, opens to the ejection chamber 23 which is equipped with the guide walls 9 for the water stream and the slit ill? for the ejection. Sea water is spouted into the ejection chamber 23 from the opening 22 and, hence, flows into the slit it). As shown in FIGS.

9 and 13, atraverse pipe 24 and a suitable number of' pipes 25 branched therefrom are disposed above the ejection chamber 23 and slightly behind the opening 22, the branch pipes communicating with the interior of the ejection chamber 23 and with the slits 10. The traverse pipe 24 is connected to a conduit 27 at the central portion which leads to a suitable source of the compressed air such as an air compressor (not shown). The branch pipes 25 are equipped with guide vanes 26, which are U-shaped in section, as shown in FIGS. 12 and 13. The air is to be ejected from the ends 28 of the vanes 26. By such mechanism, as mentioned above, air and sea water are mixed properly and spurted out.

As a matter of convenience, tor a test equipment, a test vessel of one-tenth of the dimensions of the measurements of a normal size boat was built to measure the thrust and resistance reduction by the jet. The results of the test are as follows:

I. MEASURING OF THE THRUST When the test boat Was stationary and the air tank pressure was 1.3 kg./cm. the thrust due to the jet was 550 g. (g. standing for gram) and in case the air tank pressure was 1.0 kg./cm. the thrust due to the jet was 470 g. To observe the circumstances at that time, as the boat stops, air is accumulated in layers at the bottom or the hull, while some air was poured out of the boatside in bubbles, on account of which the test boat rocks. This means that the air pressure at the bottom of the boat is higher than the water pressure at the same place. Such air pressure must become a thrust when it acts on the bottom at the slit tor ejection. The area of the step was 45 cm. and as the thickness of accumulated air layers is about twice as much as the height of the bottom step at the slit for ejection, the air pressure is raised by about 2 g. Therefore, a thrust due to the above air pressure is 90 g. For the sake of safety in this case, the increase in the thrust owing to the standstill of the boat at 100 g. is assumed, while the propelling power is in general considered to be directly proportional to the pressure in the air tank. Consequently, from the above result, the following empirical formula, constituting the average, is obtained:

Thrust (g)=360 =air tank pressure (kg/om?) (a) II. MEASUREMENT OF THE RESISTANCE REDUCTION BY JET When the speed of the above test boat is set at 6 m./sec., the resistance in case 01f movement was 5 kg. and when the speed was 7 m./sec., the resistance was 6.9 kg.

Then, the resistance is measured when the test boat moves at the speeds of 6 m./sec. and 7 m./sec. ejecting the air having the [following pressures: The results are as follows:

Speed of boat, Air pressure, Measured resistm./sec. kgJem. ance,kg.

To examine the circumstances at the time of the above test, it is recorded that air was excessive in case of 6 m./sec. of speed and 1.5 kg./cm. of air pressure. In other words, the above test was not run under the best conditions. Accordingly, the numerical value of the air pressure measured in this test can be considered that its accuracy is lower than that of other values and the data on the preliminary experiment suggest this fact.

To find an average, supposing that the accuracy weights of the above (1) and (2) and are 1 to A2, respectively, We can say that the bow Wave can be almost effectively absorbed by jetting air on which 1.17 kg./crn. or 1.2 kg./cm. of air pressure is applied, when the boat is running at a speed of 6 m./sec. or 7 m./sec., respectively.

Now, from the above results, the decrease ratio of re- Original resistance III. ESTIMATION OF RESISTANCE COEFFICIENT AND SPEED OF JET The displacement of the normal size boat in case of full load and regular load are 45 and 40 tons, respectively. The test was made in the state of a regular load. Then displacement of the test boat was 40 kg.

Using V for displacement and s for density of sea water,

To find the resistance coefficient 7 m. in case of the boat-speed of 6 m./ sec. and 7 m./sec.

The resistance curve of the test boat as shown in FIG. 16 ascertains these results.

The jet speed can be found from its thrust and the area of the slit for ejection. Using s for the density, U for the jet speed, V for the boat speed, Q for the total ejected fluid (per unit hour) and S for the area of the opening of slit,

To find the jet Speed by the above formula (8:20 cm?) If V=6m./sec. U=42.7 m./sec. (c) If V=7 m./sec. U=46.9 m./sec.

To examine the pressure and flow of the jet in accordance with the method of the present invention, the total pressure of the jet (that is, the total pressure=static pressure-I-dynamic pressure), first of all, must be larger than the average total pressure of Water steam acting on the bottom of the hull, because, in the present invention, the fluid is ejected along the bottom or boat-side to increase the speed of the water stream thereabout, to lower the pressure and to reduce the wave making resistance by evening the water pressure on the bottom and boat-side.

Secondly, a considerably wide-ranged change of the water pressure must exist in the section perpendicular to the keel line.

Therefore, the ratio of the energy given from jet to water stream per time unit and energy given from the boat to sea water per time unit should be a fixed one.

That is, using Cp, Ct for the constants,

(Total pressure of jet) =Cp (Average dynamic pressure on the ship) (I) (Thrust of jet)=Ct (Resistance of ship) (II) Cp and C! are experimentally obtained under the conditions that the effect of jet is maximized to each speed of the vessel.

And if,

U: Speed of jet s Density of jetted fluid 52 Density of sea water S: Area of a slit for ejection Q: Total ejected flow (per unit hour) V: Speed of ship V: Displacement L: Length of ship 'ym: Resistance coefiicient g: Gravity acceleration.

Resistance of ship=ymVsV then above Formula I will be,

/zs(U V =Cp'ymsV (III) and Formula II will be,

s(U-V)Q=Ctq msV /sV (IV) To find U and Q from the Formulae III and IV,

U=Vwll+2Cpi m (V) Q= V V (VI) Power causing such jet is, /2s(U ---V )Q, and the power of the boat (motive power) when the jet does not work is,

Therefore, using r for a ratio of the former to the latter,

or using Formula IV,

Supposing that the resistance was decreased by the jet to s times of the original one as mentioned in Table I, the ratio of the sum of the driving power of the improved boat and the generating jet power to the driving power of the original size boat is (VII) Op =2.07 (In case V=6 m./sec.)

1.83 (In case V=7 m./seo.)

Averaging them,

Cp=l.95

To find Ct from Formula II using the values in the abovementioned Table I,

Ct= 'g =O.084 (In case V=6 rn./sec.)

=%%: 0.062 (In case V=7 m./sec.)

To average the above,

Though Cp and Ct should be regarded as the function of the Froude number, they are treated as fixed as follows, and the following values of U/ V, r and the rate of power decrease are obtained from Formulae V, VII and X using Cp, Ct, the resistance curves in FIG. 14 and the Table I as follows:

Table II Froude number 0.6 0.8 1. 0 1.2 1. 4 1.6

m(Resistance Coeflieient)- 0.040 .028 .022 .016 .012 .012

In case aironly was jetted:

U/V 12. 5 10.5 9. 3 8v 0 6. 9 6. 9 r 0.50 0. 42 0. 39 0.33 0.29 0.29 Power decrease rate- 0. 91 0.83 0.80 0. 74 0. 0.70 In case water only was jetted- U/V 17 08 1.06 1.04 1.03 1.02 1.02 r 0.077 0.076 0.076 0.075 0.075 0 075 Power decrease rate 0. 55 0. 58 0.62 0.6 0.71 0. 71 In case of ejection of air and water mixed equally in volume:

1.15 1.10 1.09 1.06 1.05 1.05 r 0.080 0.078 0.078 0.076 0.076 0.076 Power decrease rate-.. 0. 49 0. 49 O. 49 0. 49 0.49 0. 49

Using the numerical values of Table 2 and the resistance curve in FIG. 14, the relations between the speed of the boat and the total power, which is the sum of the power for generating the jet and the driving force of the boat, as shown diagrammatically in FIG. 15 are found.

In other words, in FIG. 17 the abscissa denotes the speed of the boat and the ordinate the sum of the power required to generate the jet and to drive the boat while the curves show the relation between them, when the present invention is applied to a boat which requires a driving power of 1,000 HP. for a speed of 30 knots.

The effectiveness, as mentioned above, of the method of the present invention is taken even in case of the different types of boat because all tendencies are parallel to those of the test boat if considered on the basis of the Froude number. Accordingly, the numerical values in Table II can be almost applied to the difierent types of boats and the diagram in FIG. shows almost exactly the tendencies in that case.

In the present invention, the use of a double structure for the bottom surface of the bow or the stern and the guidance of the fluid from an air compressor or a feed water pump to the ejecting part are regarded to complicate the structure and to be of disadvantage. However, the use of a mixed fluid of air and sea water is, as already explained, of advantage. As to sea water, if it is mixed with air, a very small amount of flow is enough. The apparatus for such a small amount of water can be almost neglected structurally and the blowing structure from the air compressor can be almost disregarded in designing the vessel. Concerning the double structure of the bottom, the installation of a step in a high-speed boat has been widely adapted heretofore. By utilizing the part of such step for the part of a slit for ejection, the boat can be designed without any special difiiculty. Besides, this method, as mentioned above, can be suitably applied to the float of the flying boat, etc. By using the method of the present invention as explained above, the wave making resistance caused by running of the hull can be suitably reduced. Thus, the hull can easily and smoothly run and as the power for driving the hull can be reduced, so with a certain amount of fuel, the boat can run for a distance longer than that for which the boat is provided. Moreover, the boat can run at a high speed. Consequently, the engine for driving the boat can be simplified and diminished in size, while the load of the boat increases and the expenditures for operation can be reduced. The present invention has such many remarkable economic effects as mentioned above. Furthermore, as it reduces the waves around the bow, etc., it can increase the seaworthiness by stabilizing the bow on the surface of the sea. At the same time, if eiiectively controls pitching and enables the boat to run safely.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

I claim:

1. An apparatus for reducing the wave making resistance for boats comprising a hull having an intake on both sides of its bottom,

a first guide pipe extending into said hull from each of said intakes,

a pump disposed in said hull and receiving the inner end of said guide pipe,

said pump being adapted to be driven and to draw seawater into said intakes,

an outlet pipe connected to the output end of said said' hull including an ejection chamber,

the free end of said outlet pipe opening into said ejection chamber,

a plurality of guide walls disposed in said ejection chamber and guiding a water stream emerging from said pump through said ejection chamber,

the latter having a plurality of slits at its rear end for ejection of said seawater from said ejection chamher,

a plurality of branch pipes and a transverse pipe disposed above said ejection chamber and communicating with said slits,

said branch pipes communicating with said transverse an air compressor disposed in said hull,

a second'guide pipe connecting said air compressor 7 with said branch pipes, and

said branch pipes having guide vanes of substantially U-shaped for guiding air emerging from said air com pressor towards said slits.

2. The apparatus, as set forth in claim 1, wherein said slits are disposed near the bow of said hull.

3. The apparatus, as set forth in claim 1, wherein said slits are disposed within a range of 15% to 35% of the length of said hull measured from the bow of said hull.

References Cited in the file of this patent UNITED STATES PATENTS 632,738 OHara Sept. 12, 1899 640,946 Quanonne Jan. 9, 1900 812,656 Julhe Feb. 13, 1906 1,591,748 Dieckmann July 6, 1926 1,662,206 Paxton Mar. 13, 1928 1,775,757 Gay Sept. 16, 1930 1,822,223 Klinger Sept. 8, 1931 1,877,380 Baldwin Sept. 13, 1932 2,086,593 Wood July 13, 1937 2,218,938 Rinne Oct. 22, 1940 2,764,954 Oeltgen Oct. 2, 1956 2,954,750 Crump et al. Oct. 4, 1960 FOREIGN PATENTS 317,333 Germany Dec. 15, 1919 886,420 Germany Aug. 13, 1953 919,931 Germany May 3, 1956 2,298 Great Britain of 1915 11,023 Great Britain of 1911 20,674 Great Britain of 1906 500,739 Great Britain Feb. 15, 1939 715,880 Great Britain Sept. 22, 1954 

1. AN APPARATUS FOR REDUCING THE WAVE MAKING RESISTANCE FOR BOATS COMPRISING A HULL HAVING AN INTAKE ON BOTH SIDES OF ITS BOTTOM, A FIRST GUIDE PIPE EXTENDING INTO SAID HULL FROM EACH OF SAID INTAKES, A PUMP DISPOSED IN SAID HULL AND RECEIVING THE INNER END OF SAID GUIDE PIPE, SAID PUMP BEING ADAPTED TO BE DRIVEN AND TO DRAW SEAWATER INTO SAID INTAKES, AN OUTLET PIPE CONNECTED TO THE OUTPUT END OF SAID PUMP, SAID HULL INCLUDING AN EJECTION CHAMBER, THE FREE END OF SAID OUTLET PIPE OPENING INTO SAID EJECTION CHAMBER, A PLURALITY OF GUIDE WALLS DISPOSED IN SAID EJECTION CHAMBER AND GUIDING A WATER STREAM EMERGING FROM SAID PUMP THROUGH SAID EJECTION CHAMBER, THE LATTER HAVING A PLURALITY OF SLITS AT ITS REAR END FOR EJECTION OF SAID SEAWATER FROM SAID EJECTION CHAMBER, A PLURALITY OF BRANCH PIPES AND A TRANSVERSE PIPE DISPOSED ABOVE SAID EJECTION CHAMBER AND COMMUNICATING WITH SAID SLITS, SAID BRANCH PIPES COMMUNICATING WITH SAID TRANSVERSE PIPE, AN AIR COMPRESSOR DISPOSED IN SAID HULL, A SECOND GUIDE PIPE CONNECTING SAID AIR COMPRESSOR WITH SAID BRANCH PIPES, AND SAID BRANCH PIPES HAVING GUIDE VANES OF SUBSTANTIALLY U-SHAPED FOR GUIDING AIR EMERGING FROM SAID AIR COMPRESSOR TOWARDS SAID SLITS. 